Most ink-jet printers employ integrated printhead cartridge units which house both an ink dispensing printhead or pen and one or more ink supply reservoirs. A single ink reservoir generally is provided in a monochrome cartridge containing black ink, and three separate ink reservoirs are provided in a tricolor cartridge containing colored inks. The ink reservoirs on printhead cartridges have not heretofore been designed for refilling. Nevertheless, refilling devices have been marketed which allow users to replenish the ink in certain types of cartridges. One such refilling device employs a syringe having a needle that is inserted into the air vent hole on top of a cartridge. Ink is forced into the reservoir via the needle. Syringe-type mechanisms can be messy, requiring the user first to fill the syringe from an ink bottle and then to transfer it to the cartridge. It is also easy to overfill the cartridge using a syringe.
Despite the drawbacks of existing ink-jet printhead cartridge refill mechanisms, replenishing the ink in the cartridge reservoir is desirable. Refilling is usually more economical than replacing the cartridge each time the ink is exhausted. It also avoids the premature disposal of the cartridge itself, allowing it to be re-used multiple times. What is needed, however, is a reliable ink refill system for cartridges that eliminates the messiness of prior art syringe refill devices, thereby further encouraging refill and reuse of printhead cartridges.